Such devices are known, and comprise an engine-cooling loop in which a heat-carrying fluid circulates which takes up heat from the engine and which gives it back to an air heater, a heat-pump loop in which a refrigerant fluid circulates, this loop containing a compressor, an evaporator constituting a cold source of the heat pump at which the refrigerant fluid takes up heat from the surroundings, and a condenser constituting a hot source of the heat pump at which the refrigerant fluid gives up heat, the condenser being integrated into the engine-cooling loop upstream of the air heater.
In motor vehicles, whether they are internal-combustion-engine, electric or other vehicles, the main heating of the passenger compartment is carried out by means of an engine-cooling loop which takes up heat from the engine and transfers it to a heat exchanger, called air heater, swept by an airflow which is directed into the passenger compartment.
However, it can happen that this heating proves to be insufficient, for example if the outside temperature is particularly low. This comes about, more particularly, when the vehicle is equipped with a modern, high-efficiency engine in which the thermal losses are low, which does not allow a sufficient quantity of heat to be extracted from it.
It is for this reason that it is known to equip motor vehicles with supplementary heating, which makes it possible to contribute supplementary heating to the passenger compartment in situations in which the main heating proves to be insufficient.
Auxiliary-heating boilers are known, which are integrated into the cooling circuit upstream of the air heater. This makes it possible to increase the temperature of the engine-cooling liquid upstream of the air heater, and consequently the temperature of the airflow delivered by the latter. The drawback of such a device is that the temperature of the cooling liquid is also increased upstream of the engine. Consequently, the quantity of heat extracted from the engine reduces. This reduction has to be compensated for by the boiler, which reduces the quantity of additional heat available for heating the passenger compartment. The energy efficiency of such a device is therefore hardly satisfactory.
The Japanese document JP 10-76837 (Calsonic) describes a device for heating the passenger compartment of a motor vehicle including a cooling circuit with which is associated a supplementary-heating circuit which forms a heat pump, by virtue of which heat is taken up at a cold source by evaporation of a fluid in an evaporator, and this heat is transferred to a hot source by condensation of the same fluid in a condenser. A heat exchanger constituting the cold source of the heat pump is integrated into the cooling circuit upstream of the engine, and a heat exchanger constituting the hot source of the heat pump is integrated into this same circuit upstream of the air heater. The refrigerant fluid of the heat-pump loop gives up heat to the heat-carrying fluid upstream of the air heater.
In such a device, the temperature of the heat-carrying fluid of the cooling circuit is not increased at the inlet to the engine. In contrast, it is lowered by the take-up of heat at the cold source of the heat pump. That being so, the quantity of heat extracted from the engine is not reduced, but increased. The energy efficiency of the top-up heating is markedly enhanced by comparison with a device such as the one which was described previously.
However, this device exhibits several drawbacks. On the one hand, it does not allow cooling of the passenger compartment in the case of a high outside temperature. Moreover, the heat taken up from the cooling circuit, in heating the refrigerant fluid of the heat pump, can lead to an inadmissible intake pressure for the compressor, which can lead to it being destroyed.
The object of the invention is especially to remedy these drawbacks. It proposes a heating and/or air-conditioning device which makes it possible to cool the passenger compartment in the event of high outside heat. Moreover, this device makes it possible to control the pressure of the fluid in the heat-pump loop at the inlet to the compressor.